This invention is an improvement over U.S. Pat. No. 7,308,968 (the '968 patent) for a transportable rescue conveyer in that it provides unique powered aerial ladder mechanism that extends the stiles of the ladder to reach a building, ship or oil-drilling platform and also moves the rungs to raise and lower the fireman, a person rescued, and any load the fireman may need to raise or lower with him. Unlike the '968 patent, this improvement provides a powered ladder for a fire and rescue truck that more closely resembles traditional manual-climb ladders, except that it multiplies the lift and rescue potential of fire and rescue personnel. The present invention is distinctly different from the '968 patent in that a single specially designed boom is used that supports and guides the rungs and enables their movement in a loop in a forward or backward direction.
The notion of movable rungs was disclosed for an electrically adjustable ladder in U.S. Pat. No. 5,145,031 (the '031 patent). While not an aerial ladder, the '031 patent teaches the use of threaded screws extending along two parallel stiles through which the rungs are mechanically connected. The present invention does not use the mechanism described in the 031 patent.
U.S. Pat. No. 4,467,889 (the '889 patent) teaches a ladder-guided service elevator to carry persons up or down along a building wall or other structure. The service elevator is not an aerial ladder but rather is similar to a traditional ladder, which must be secured to a structure. The structure then supports an endless conveyor band that engages the rungs of the ladder and the elevator that carries a load up and down. There is no mechanism for extending the ladder-guided elevator or for its operability upon such extension.
Vehicle-mounted retractable ladders without movable rungs are also well known and are common in fire and rescue vehicles. An example from 1982 is U.S. Pat. No. 4,317,504 for a telescopic aerial ladder, especially intended to be mounted on a transportation vehicle. The ladder comprises a number of ladder members superposed atop each other, each member consisting of two trapezoidal lateral wings connected by rungs. The upper and lower longitudinal edges of each member are not in parallel relationship but designed in such a manner that the distance between said edges is increasing towards the end of said member which remains imbedded within the corresponding end of another ladder member which is located near below said member. The present invention's telescopic mechanism is distinctly different in that the telescoping ladder sections are nested within each other, providing for very compact storage atop the vehicle.
A recent example of a non-emergency vehicle application of a retractable ladder is U.S. Pat. No. 5,064,022 (the '022 patent). The '022 patent teaches a ladder apparatus and method for use with large construction equipment, such as large tractors, mining trucks and similar vehicles that have an operator's platform or operating station located a substantial distance off the ground. The powered ladder has a fixed ladder portion rigidly attached to the vehicle. While typical, such ladder mechanisms are distinctly different from the present invention in both structure and capability provided by a unique movable rung system.